One welt known method of planning a trip using a given route is to mark the route on a paper map or chart and then refer to the marked route whenever a route decision point is reached. This approach assumes that the traveler is using a well marked route, among a network of such routes, that is easily visually perceived. If the route is not part of an easily perceived network, or if the traveler is visually impaired or unfamiliar with the region, a route marked on a paper map or chart may be of little use.
Several patents disclose portable navigation devices for walkers that combine pedometers and direction finders. One such navigation device is disclosed in U.S. Pat. No. 3,355,942, issued to Freeman, for a fully mechanical stride measuring device that relies upon air pressure variations sensed in a bellows carried in one or both heels of the walker's shoes. As the journey progresses, each step (or every other step) of the walker produces an compression/expansion cycle in the bellows, and the number of such cycles is accumulated to determine total distance travelled, based upon an average length stride for that walker. The direction finder determines the present bearing of the walker and expresses each stride in terms of north, east, south and west components. The path followed by the walker and the walker's present position relative to his/her path origin are thus determined.
Another portable navigation device is disclosed by Hoff in U.S. Pat. No. 3,710,083. Present direction of travel is determined by an electronic compass that generates voltages proportional to the horizontal and vertical components of the Earth's local magnetic field. The output signal is processed further and multiplied by a voltage signal representing the distance travelled by the walker at each stride to determine the north, east, south and west components of each stride of the walker. The local directions for magnetic north and true north are reconciled with each other. A distance measuring device for each stride is introduced but not discussed in detail.
U.S. Pat. No. 4,220,996, issued to Searcy, discloses a portable distance computer to be worn by a walker or runner. Path direction is not determined; only the total distance travelled is determined. The device displays the pre-selected number of strides to be taken per unit time interval and provides an audible tone for each stride to be taken at that stride rate. A visual stride cue, such as a blinking LED, can also be provided. The device also displays the present time or elapsed time and the number of minutes per mile, computed using an adjustable stride length. Another electronic pedometer that computes and displays distance travelled, time per unit distance, elapsed time and time of day is disclosed by Karr et. al. in U.S. Pat. No. 4,371,945.
Elbaum et. al. disclose a curve follower that uses a a grid of intersecting lines in U.S. Pat. No. 4,319,331. Coordinates of the curve where the curve crosses a given line or set of lines are recorded and used to quantize the curve into a sequence of line segments. The grid may be two- or three-dimensional. The curve to be followed or described may be set down on a plane, on a two-dimensional surface, or in a space frame. Endpoints of a curve possess special characteristics that allow identification as such.
Tanaka et. al., in U.S. Pat. No. 4,608,656, disclose a road map display system that indicates the position of a selected vehicle. The system includes a plurality of scalable maps of adjacent regions and means for choosing a particular scale factor for the map displayed, especially where the vehicle approaches an intersection or possible decision point in the path followed. A map is displayed with an icon representing the vehicle, and the vehicle is displaced from its starting point as the vehicle journey proceeds.
Another scalable map display system for a vehicle is disclosed in U.S. Pat. No. 4,675,676, issued to Takanabe et. al. A map showing the present vehicle location can be scaled automatically as the vehicle approaches the specified destination; or the displayed map can be scaled by a user-selected factor.
In U.S. Pat. No. 4,821,192, Taivalkoski et. al. disclose a map system for a moving robot, defined by a sequence of nodes that determine the path to be followed by the robot. The distance the robot has travelled along the selected path is measured at certain intervals. The final node representing the end of the selected path has a beacon that radiates a signal perceptible by the moving robot. The robot learns the selected path as an ordered sequence of path segments having direction and length in that direction. The system can also monitor the robot's orientation along the selected path. The robot apparently halts when it reaches the beacon. The path to be followed by the robot can be internalized or stored in memory by the robot, as a sequence of path segments having both length and direction.
Baird, in U.S. Pat. No. 4,939,663, discloses use of a topographical map for navigational correction of the computed flight path of an aircraft. A topographical map of the surface along the intended flight path, including a grid of elevations, is stored in a computer. A sequence of altimeter readings taken during the flight are compared with the estimated aircraft flight path, and corrections are determined based upon the most probable aircraft position consistent with each altimeter reading.
A map display for a moving vehicle is disclosed by Nagashima in U.S. Pat. No. 4,970,682. A distance sensor and a direction sensor estimate the distance and direction travelled and relate these to a road map or path stored in a computer, using pattern recognition techniques. An icon representing the vehicle's estimated present position along the selected path is displayed from time to time.
U.S. Pat. No. 4,991,126, issued to Reiter, discloses a portable, automatic orientation device for walkers, runners and horseback riders and for the blind. A stride motion pulse generator senses each step taken by the walker, runner or rider and, using an average distance for each such step, accumulates the number of steps taken and the distance travelled since the wearer of the device left the "origin". A local magnetic field sensor determines the direction taken for each step and determines the two-dimensional vector representing that step in a local tangent plane on the Earth's surface. The particular path taken from origin to destination is stored and can be retraced by the device wearer, using a visual or auditory readout from the device to stay near or on the path originally taken. The device does not use a map or accept entry of path information from a map and does not provide information on the wearer's present location as the journey progresses. The device is small and can be worn around the waist or around the neck of the user.
Schneyderberg Van Der Zon, in U.S. Pat. No. 4,996,645, discloses a map display system in which road map data are stored and selectively displayed, together with a name representing the local area, for vehicle navigation. A portion or all of the road map data for a local area can be displayed. The system includes a vehicle direction indicator and a distance travelled indicator so that the local area including the present location of the vehicle can be automatically called up and displayed. The map detail representing the local area can be displayed in different colors. The origin and destination of a trip are entered by a keyboard included in the system. The keyboard can also be used to request display of a specified local area.
Control of a route taken and operations performed by a wandering robot, using electronic chip cards loaded into the robot's memory, is disclosed by Gloton in U.S. Pat. No. 5,031,109. With one or more such cards loaded into the robot's memory, the robot follows a path prescribed by the card(s) and performs operations prescribed by the card(s) at specified locations along the route. The route taken and the operations performed can be changed by changing the cards loaded into the robot's memory.
A navigation system for land vehicles, using stored road map data, is disclosed in U.S. Pat. No. 5,122,961, issued to Toyama et. al. The system includes a direction sensor and a distance travelled sensor to determine and display the present location of a vehicle along a selected route. Using the selected route and road constraints set down in the stored road map data, the present vehicle location is computed and displayed. Two spaced apart photosensors that also emit light are directed at the road passing beneath the moving vehicle and are used to detect or check actual vehicle speed.
The above-described approaches do not provide the accuracy needed for a route that is not part of a network of easily perceived routes, do not provide automatic prompting as a traveler approaches a route decision point, and/or or not portable. What is needed is a portable mapping or charting system that: (1) allows use of any two-dimensional map or chart for planning the chosen route, including commercial maps and reproductions thereof and electronically displayed maps; (2) provides information on a chosen route that is accurate to within a few meters; (3) provides automatic visual or audible prompting of the traveler as a decision point in the chosen route is approached; (4) can be used where the chosen route is part of a network of easily perceived routes or in a region (i.e., the wilderness) where the route is not so perceivable; (5) allows change of a route to a chosen alternative route if some portion of the original route is impassible or otherwise unavailable; (6) provides audible and/or visual prompting as the traveler's deviation from from the chosen route becomes significant and indicates the direction and distance required to return to the chosen route; and (7) allows use of bar code or other suitable means for entry of information to fix the map scale and relevant details in the system's frame of reference.